With intent to analyze characteristics of a substance, a measuring method has hitherto been used which includes the steps of holding a specimen to be measured on an aperture array structure, applying an electromagnetic wave to the aperture array structure on which the specimen is held, and analyzing a transmittance spectrum of the electromagnetic wave, thereby measuring the characteristics of the specimen. One practical example is a method of applying a terahertz wave to a metal mesh filter, for example, to which a specimen, such as a protein, is attached, and analyzing a transmittance spectrum of the terahertz wave.
Through the studies made by the inventors, it is known that sensitivity in detection of the specimen has a tendency to increase by employing an electromagnetic wave of a shorter wavelength. In the case using the electromagnetic wave of the shorter wavelength, however, the thickness of the aperture array structure requires to be reduced, and it becomes the order of about 100 nm to 20 μm, for example. Forming such a thin metal mesh or the like in shape of several millimeters or several centimeters square in a not-flexing state is very difficult to realize in practice.
For that reason, when the aperture array structure being so thin is used, a support base (e.g., a resin film) to which the aperture array structure is bonded for fixation is needed in order to keep the aperture array structure in the not-flexing state.
Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2007-010366) discloses a method of holding a specimen to be measured on an aperture array structure (e.g., a metal mesh) having an aperture region and on a base in close contact with the aperture array structure, applying an electromagnetic wave to the aperture array structure on which the specimen is held, and detecting the electromagnetic wave having transmitted through the aperture array structure, thereby measuring characteristics of the specimen based on a change of frequency characteristics, the change being caused due to the presence of the specimen. One of principal surfaces of the aperture array structure is in a state entirely bonded to the base. Furthermore, the base in Patent Document 1 is used to primarily to make the specimen adsorbed to the base. In some cases, a material capable of selectively adsorbing the specimen may be coated over the base in advance.
In the case using the support base mentioned above, however, a problem arises in that one 10b of principal surfaces 10a and 10b of an aperture array structure 1 is in a state entirely bonded to a support base 2 as illustrated in FIG. 14, and hence the specimen cannot be held on the one principal surface, whereby a region near the principal surface of the aperture array structure where sensitivity is maximum cannot be efficiently used for the measurement. Stated in another way, in the measuring method described above, a change of frequency characteristics is caused due to the interaction between an electromagnetic field localized on the surface of the aperture array structure and the specimen. The intensity of the localized electromagnetic field is maximal in regions near both the principal surfaces of the aperture array structure, and it attenuates exponentially as a distance from both the principal surfaces increases.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-010366